Plastic bristles which are extruded are normally smoothed on their surface due to the manufacturing process. In the case of brushware of a random nature, such bristles exercise their brushing action initially and mainly through the free ends of the bristles, which tear open the dirty surface and remove the dirt by scratching and scraping. In the case of stronger pressure, the bristles are bent round and act with their circumferential surface. They then slide in a stroking and sliding manner over the surface with a more gentle action. Also when applying paint and the like by means of a brush the bristles are curved or bent, so that they engage with the surface to be treated not only with their free bristle ends, but also with their circumferential surface. For a long time consideration has been given to using the circumferential surface of the bristles for surface treatment purposes by structuring or profiling it.
East German patent 32963 and U.S. Pat. No. 2,642,705 disclose the application of abrasive particles to the circumferential surface of bristles or a bristle material by embedding the same in the surface melted-on bristle material. Such a procedure is not only very complicated, but it has also been found that the external abrasive particles can become loose in particular due to the bending action occurring when using the bristles. In addition, such bristles are so abrasive and therefore aggressive, that it is not possible to use them in all cases of human dental and body care.
It is known from U.S. Pat. No. 2,642,705, British patent 1 327 329 and in particular DE-OS 20 37 674 to incorporate by mixing abrasive particles into the plastics material of the bristles. According to DE-OS 20 37 674 inorganic abrasive particles of aluminium oxide, chopped glass fibres, asbestos particles or ceramic material or also diamond particles are used, which have a much greater hardness than the surrounding plastics material, so that there is a very pronounced abrading action, which in many cases is undesired. Frequently the abrasive particles are incorporated in such a high percentage that they touch or penetrate to the bristle surface. Experience has also shown that such embedded abrasive particles over a period of time are exposed as a result of wear on the surface of the bristle, so that the abrasiveness of the bristles is significantly increased, so that such bristles cannot be used for human dental or body care, because it would lead to considerable risks of damage to the skin, teeth or mucous membranes of a user. In order to e.g. remove plaque from teeth or dirt from floors or roads, it is not so much a question of obtaining an abrading action by abrasive material, but instead a so-called reaming action, which could be achieved by a surface structure or topography. Through the mixing in of abrasive particles such a surface structure can only be obtained when using relatively large particles. Admittedly the reaming characteristics of such a bristle are adequate, but the large abrasive particles projecting over the surface simultaneously lead to high abrasiveness. The bristles are also greatly weakened by the incorporation of large abrasive particles, so that the bristles only have an inadequate strength.
It is also known to mechanically roughen the surface of bristles, in that the bristle flanks are structured with a tool (U.S. Pat. Nos. 3,325,845 and 3,229,347). The roughening of the bristle flanks can be brought about by means of an abrading or grinding device or also by sand blasting. However, this leads to the disadvantage that the longitudinally oriented molecules in the bristles are torn open and consequently the bristles are weakened. This procedure is also very complicated. After working the surfaces become fibrous and fringy, which leads to the risk of parts being released from the bristle material. It has been found that it is not possible in this way to obtain a clearly defined surface topography.
EP 360 938 A1 proposes embedding a blowing agent in the bristle material and to bring about a surface roughness by foaming the blowing agent. However, the chambers or cavities forming throughout the bristle strand lead to a significant bristle stiffness reduction. In addition, due to the torn open cavities the bristle surface is non-uniform and has no clearly defined structural depth or topography, which is necessary for effective reaming.